import java.net.*;
import java.io.*;
public class UDPServer{
    public static void main(String[] args){
        DatagramSocket aSocket = null;
        try{
            aSocket = new DatagramSocket(6789);
            byte[] buffer = new byte[1000];
            while(true){
                DatagramPacket request = new DatagramPacket(buffer,buffer.length);
                aSocket.receive(request);
                DatagramPacket reply = new DatagramPacket(request.getData(),request.getLength(),request.getAddress(),request.getPort());
                aSocket.send(reply);

            }
        }catch(Exception e){
            System.out.println("error");
        }
    }
}

